Christine Powell Research

My research interests center on understanding why earthquakes occur in continental
intraplate seismic zones. I approach this interesting problem using local travel time
tomography to investigate the seismic velocity structure of the crust hosting the
seismic activity. To date, P wave and S wave velocity models and Vp/Vs ratios have
been determined for four intraplate zones: the Charlevoix seismic zone located near
Quebec, Canada, the 2001Bhuj India aftershock zone, the eastern Tennessee seismic
zone (ETSZ) and the New Madrid seismic zone (NMSZ). A common observation in all four
zones is that strong velocity contrasts are present and that these contrasts appear
to control the distribution of seismicity. The results suggest that earthquakes in
intraplate seismic zones tend to occur in rocks where strain energy is concentrating.
The Vp/Vs results for the NMSZ are particularly interesting. Low Vp/Vs ratios are
associated with the main branches of seismicity to depths of at least 9 km. The cause
for the low ratio values remains an open question. I am also using gravity and magnetic
data to investigate crustal structure associated with the ETSZ. Potential field data
along several cross sections were inverted to determine possible fault parameters,
rock densities and susceptibilities, and plausible source rocks. The models suggest
that the seismicity is associated with a Grenville-age suture zone that juxtaposed
crustal masses with different lithological properties. Ongoing research projects involve
application of double-difference tomography to determine source locations and velocity
structure in the ETSZ and the NMSZ.

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